Image enhancement systems generally comprise four major sections in addition to the computer or central control section. They are the image acquisition section, the image processing section the storage section and the image display section. It is the purpose of the image processing section to effect the enhancement of the image that is displayed. Many times the steps taken to enhance one characteristic of the images have adverse effects on other characteristics of the images. When this occurs trade offs and comprises in the enhancement process are effected. In such cases neither characteristic is optimized. Thus improvements in the enhancement equipment or methods that avoid previously necessary trade-offs or compromises are continuously needed, sought after and desired.
In digital fluorography the video signal output of the image acquisition section is amplified at the input of the image processing section. To begin the enhancement procedure, in the past, the amplifier used in digital fluorographic (DF) systems were log amplifiers because of the exponential nature of the intensity signal. Log amplifiers operate to provide radiation intensity attenuation (object density) signals that are linear. The linear signals are a function of the intensity of the signals passing through a blood vessel under study.
However, as is well known, log amplifiers have extremely high gain around the zero point. Therefore any error or noise occurring near the zero point is greatly amplified. The amplification of the noise and errors in fact resulted in the abandonment of the "log amplifier" by most of the industry. Instead those skilled in the art opted for using the analog to digital converter on the "linear" signal from the intensifier in conjunction with look up table arrangements for the line to log conversions. However this option loses the inherent benefits of using a log amplifier on signals having exponential characteristics--if the zero neighborhood amplification problem could be solved.